Instead of spamming the idea in the three different Legion class threads I figured I'd just make a new one. This isn't about Soulburn: Haunt (bye Felicia), just the Soulburn spell.
The return of Soul Shards to all three specs in Legion also coincides with the removal of a key related spell: Soulburn. If you've already forgotten what Soulburn does, it consumes a Soul Shard, and in return it empowers the next spell cast with some form of added utility (only a few spells left on Live gain any kind of empowerment). Mostly it is just used as part of the Soulburn: Haunt priority list.
The benefit of Soulburn is that it exchanges some throughput for increased utility in one form or another, which is a mechanic that Blizzard has seemed to like (Destruction on Live exchanging a Chaos Bolt for an Ember Tap, Ret using Holy Power on Word of Glory rather than Templar's Verdicts, etc.).
With that in mind, I propose not just a return of Soulburn in Legion, but an expansion of its usefulness. Since we're no longer limited to just one spec using Soul Shards, it would be work that all three specs could benefit from. Without wasting any more bandwidth, here's my list of possible Soulburn uses:
Class-wide Soulburn effects:
Soulburn + Fear = Removes all Damage over Time effects from the target.
[or merely all of the Warlock's Damage over Time effects.]
Soulburn + Health Funnel = Health Funnel is no longer channelled, but leaves a 20 second Heal over Time effect on the targeted Demon.
OR
Soulburn + Health Funnel = Health Funnel can be cast on other players at reduced efficiency.
Soulburn + Summon Demon = Makes your Summon Demon spell instant cast.
OR
Soulburn + Summon Demon = Reduces the cast time on your Summon Demon spell by 3 seconds.
[Return Summon Demon spells to their current baseline of 5 seconds with no innate Soul Shard cost.]
Soulburn + Eye of Kilrogg = Increases the movement speed of your Eye of Kilrogg by X%.
OR
Soulburn + Eye of Kilrogg = Your Eye of Kilrogg can now melee enemy targets.
Soulburn + Drain Life = Increases healing done by your next Drain Life by X%.
OR
Soulburn+ Drain Life = Drain Life instead creates an absorption shield based on the amount it would have normally healed.
[Somewhat redundant with Affliction's Soul Leech effect.]
Soulburn + Life Tap = Reduces damage taken by X% for 5 seconds.
[Redundant with Life Tap damage reduction Artifact trait.]
OR
Soulburn + Life Tap = Life Tap no longer consumes health, but instead absorbs X amount of total healing received for 30 seconds. This effect stacks.
[Copy of current Glyph of Life Tap.]
Soulburn + Soulstone = Your Soulstone cast is instant.
OR
Soulburn + Soulstone = The target of Soulstone is returned to life with 100 percent health and mana.
[Copy of current Glyph of Soulstone.]
Soulburn + Unending Breath = Unending Breath allows the target to walk on water.
OR
Soulburn + Unending Breath = Increases swim speed by X%.
[Copy of current Glyph of Unending Breath.]
Soulburn + Banish = The duration of Banish is doubled.
OR
Soulburn + Banish = Banish is no longer limited to Demons, Abberations and Elementals.
Soulburn + Unending Resolve = Damage reduction of Unending Resolve increased by 10 percent and duration increased by 2 seconds.
Affliction specific Soulburn effects:
Soulburn + Seed of Corruption = Your Seed of Corruption detonation effect will afflict Corruption on all enemy targets.
[Seed of Corruption would no longer spread Corruption as a baseline effect in Legion, probably not a popular idea now.]
OR
Soulburn + Seed of Corruption = The radius and damage of your Seed of Corruption detonation is increased by X%.
Demonology specific Soulburn effects:
???
Destruction specific Soulburn effects:
Soulburn + Rain of Fire = All targets struck by Rain of Fire will be Immolated.
OR
Soulburn + Rain of Fire = Radius and damage of Rain of Fire increased by X%.
[Rain of Fire no longer costs Soul Shards baseline. Or maybe we can just get real Fire and Brimstone back with Soulburn Immolate and Soulburn Incinerate?]
Anybody want to see this spell return in Legion or are we all happy for the keybinding space? I'd love to see more utility ideas if people are interested. I know the frequency with which Demonology can gain Soul Shards kind of throws things for a loop.